To date, enzymes have been widely used in medicine. Pancreatic enzymes have been used in digestive disorders since nineteenth century. Most enzymes are used extracellularly for topical applications (e.g., collagenase), removal of toxic substances (e.g., rhodonase), and disorders within blood circulation system (e.g., urokinase). In addition, enzymes have a major potential application in treatment of cancer, e.g., asparagenase in the treatment of lymphocytic leukaemia. However, enzyme applications in medicine are limited by and suffer from following limitations. First, nature enzymes are normally lack of high selectivity to interfere only with disease related metabolic reactions, but also the normal metabolic reaction in a human body. Therefore, enzyme-based drugs (except for those orally administrated digestive enzymes) can lead to significant side effects. Second, enzymes are antigenic, and can elicit immune response in the patient, especially on prolonged use. Third, most enzymes have short effective life in the circulatory system, and very poor stability in endosome during cell entry.